Testosterone is crucial for male health, influencing everything from men’s muscle mass to their mental health. But discussion of the male sex hormone is shrouded in confusion, leaving men worryingly ill-informed. How does testosterone shape a man’s health? Are testosterone levels really dropping? What are the symptoms and causes of low testosterone? And how can men protect their hormonal health?

To find the answer all men need, we spoke to Dr Richard Quinton, Consultant Endocrinologist at Newcastle Hospitals Trust and Senior Lecturer at the Translational and Clinical Research Institute at Newcastle University. Dr Quinton has published over 200 research papers, and he has helped to draft national and international guidelines for the treatment of low testosterone, making him a key authority on this vital issue.

Based on the latest research into testosterone, what is your main message for men worried about their testosterone levels?

At the moment you have the unreasonable fears and the unreasonable aspirations. The unreasonable fears are that testosterone causes everything from prostate cancer to aggression and heart disease. But you also have unreasonable expectations, which is that everyone, no matter what state they are in, or how old they are, should have the highest level of testosterone, and that testosterone is the cure-all. There is enough evidence to disperse all these unreasonable fears and expectations. But it is a matter of getting the message out.

Let’s start with the basics: when does testosterone first shape the life of a male?

Testosterone is fundamentally what in the womb turns us into males. The foetus in the womb, if it isn’t exposed to any hormones, is just going to grow to be externally female. That is it. It doesn’t matter what the chromosomes are. If the foetus doesn’t have a testis, or has a genetic mutation which means that it can’t “see” testosterone because of a receptor defect, then the baby born will be externally female.

There is also what is known as a “minipuberty” effect. So the male reproductive axis, which is active in adulthood and quiet in childhood, is actually pretty active during the last month of pregnancy, and for the first 4-5 months after birth. And that’s why baby boys may have little “stiffies” in the morning when you change their nappies, or they may have some acne. In fact, [their] testosterone may actually be higher than that of their exhausted fathers!

Baby boys, thankfully, don’t grow big testes and don’t make sperm because at that stage in life the Sertoli cells in the testes, which are the ones that drive sperm production, haven’t yet developed a testosterone receptor, so they can’t “see” testosterone. And they don’t develop body hair, because at that stage in life they don’t carry any of the skin enzymes which convert testosterone to the more powerful dihydrotestosterone (DHT). So if you get someone with severe [testosterone] deficiency during development, they may be born externally female, or with ambiguous genitalia, or with undescended testes.

Only testosterone produced in the testes can aid sperm [but] testosterone taken exogenously will impair fertility”

Dr Richard Quinton

What role does testosterone play during male puberty and adulthood?

Testosterone is what kicks off puberty in boys. Compared to puberty in girls, which is oestrogen-dependent, you are building more muscle and building bigger and stronger bones. You are building more red blood cells too. Men have about 20% more red blood cells than women, or the children of any sex, and that’s driven by the effects of testosterone. That’s also why some athletes who abuse testosterone [for doping] give blood surreptitiously, in order to keep their red blood cell count within tolerable margins, to out-guess WADA [World Anti-Doping Agency].

Testosterone is also important for external sexual differentiation, for developing body hair and for your sex drive. It’s also essential for fertility. But in order to achieve fertility, testosterone has got to be produced in the right place – by your own testes themselves. When someone takes anabolic steroids to put testosterone into the system [for enhanced performance or physical gains], these high levels are perceived by the pituitary gland. So it will dial down production of LH and FSH [luteinizing hormone, and follicle-stimulating hormone, which are important for testosterone and sperm production] and that takes the gas off the Sertoli cells. So although you have increased testosterone levels in circulation, you’ve tanked the levels in the testes. Only testosterone produced in the testes can aid sperm. Whereas testosterone taken exogenously will impair fertility.

Some studies suggest testosterone levels in men are falling. Others suggest not. Are they declining? And why is it hard to get a consensus?

One of the problems with doing these kinds of studies over time is that testosterone assays [test analyses] change. So you try to compensate for that by calibrating your testosterone assay with the previous one. But it is not infallible. And the other thing is if you are analysing stored serum, the more you store it, the more of it evaporates. And as it evaporates, the testosterone becomes more concentrated [making older samples seem higher]. So there are lots of problems with that. But certainly if you see the population become more and more obese over the last 20-30 years, a decline in testosterone level is exactly what you would expect.

Will most healthy men maintain good testosterone levels as they age?

About 2-3% of older men lose testosterone production, but the majority maintains it. These men [with low testosterone] won’t necessarily complain of sexual dysfunction, but they might turn up [with symptoms] in a fertility clinic, or in an osteoporosis clinic with fractures or unexplained anaemia, and most of these men aren’t really getting diagnosed.

We know that the overwhelming decline in testosterone with age, aside from that 2-3% I mentioned, relates to just the accumulation of illnesses and medication and obesity as men get older. So it is not directly an ageing effect. It is the ill health baggage that comes with getting older – and particularly obesity.

We see that from the European Male Aging Study (EMAS). But also the SPECT-China study mirrors the EMAS data into middle age, but when you look at older Chinese men – apart from the 2-3% I mentioned – they have testosterone levels similar to the younger Chinese men. So it seems to be a generational thing. Older Chinese men never got into Western diets, they carried on doing exercise, they worked hard, they never got obese… So we think about it as inevitable, but it’s not necessarily so.

It [low testosterone] is to some extent lifestyle-mediated, but also bad-luck mediated: if you get heart failure or pneumonia or schizophrenia or multiple sclerosis, these things are going to make you ill. So after age 40, one man in 1000, per year, develops new onset testicular failure. But this is not the usual thing. Absolutely not. No. Even in those men who do have falls in testosterone levels, due to ill health or obesity, we know that what puts everything right is if you address the underlying problem.

The big jump in testosterone prescribing in recent years has been in middle-aged men, who are probably the wrong target”

Dr Richard Quinton

So low testosterone is often the result, not the cause, of men’s health problems?

In many cases, yes. Deficiency of any hormone can make you fatigued. And some people get fixated and become convinced that it is this particular hormone that is the problem. But if you are a guy in your 40s and you are feeling tired, what is the chance that low testosterone resulting from hypogonadism (a reduction of hormone secretion) is the cause of fatigue? It’s pretty low. But if you don’t look, you don’t find.

What symptoms and tests are required to confirm low testosterone?

So the important thing is that the first blood test is done under controlled conditions. Fasted. At nine in the morning. And after a good night’s sleep. It is really easy to measure a low testosterone level. That can be done by doing a blood test in the afternoon or evening, when you’re unwell, after a big meal, or after a poor night’s sleep. Any form of physical or psychiatric illness is found to be associated with a low testosterone level. It doesn’t mean you are hypgonadal. You might be, but it doesn’t mean you are.

But there are a number of clues [for low testosterone]. If you have anaemia, or osteoporosis of if you have sexual dysfunction or infertility, or you develop painful breasts, or menopausal symptoms like flushing or sweating. But do remember, if you have a normal level of haemoglobin – your red blood cell count – and normal fertility, it is unlikely that you are hypogonadal.

Which age group of men should be most alert to low testosterone levels?

The big jump in testosterone prescribing in recent years has been in middle-aged men, who are probably the wrong target. If it were being matched according to prevalence, it should be up in older men. It seems that these older men aren’t saying the things that will trigger concerns in the doctors that they see.

Men fall into two categories. One category is men who might assume that testosterone is among the baggage. A man might go to their GP with a loss of erections or libido. So they are already thinking at the back of the mind that testosterone might be amongst the treatments for them. Whereas if you are a man who has a fracture or has anaemia, to them if a doctor says you need testosterone it sounds a bit left field.

In terms of treatment, broadly speaking there are testosterone gels which you apply once a day, and testosterone injections which are short-acting and tend to run for 21 days, and others which are more long-lasting and can last three to six months.

What is deemed a “normal” testosterone level?

This would be a very easy question to answer in the USA. Because in the USA there are only four commercial testosterone assays, and they are all cross-referenced with central assets at the Centres for Disease Control and Prevention in Atlanta. So whatever normal range they quote, that is your range. And the normal range encompasses 95% of men.

But in the UK, there are probably around seven different testosterone assays used in labs around the country. We know that some are less good than others. The way things work is that if you have a hospital laboratory, your job is to get the best deal for the taxpayer. In the same way that your cable TV comes as a bundle, with good channels and rubbish channels, so do lab tests. So you’ll go for a given provider to do tests across the spectrum. And if one test provider does a fantastic deal, and does great assays on everything except testosterone, you might have to live with that.

There is also an issue on where the “normal” ranges come from. Some bigger hospitals develop their own ranges, based on age and in-house sampling. Others will take a reference range provided by the manufacturer – and you have no idea where that comes from. So this is an issue in the UK that my special society is currently dealing with. It is our big job.

Testosterone is the lowest grade of controlled drug. There are no restrictions on who can who can prescribe it. So beware”

Dr Richard Quinton

Many men are turning to private clinics for testosterone treatment. Is this a positive or problematic development?

Men should also be aware that there are a raft of private clinics out there who will basically prescribe testosterone on demand, without any rigorous diagnostics. And testosterone is the lowest grade of controlled drug. There are no restrictions on who can who can prescribe it. So beware. Seek competent medical care. Accept the possible other causes for the problems that you’re experiencing. My own view would be to avoid seeing any specialist who doesn’t also do an NHS clinic. If the person you are seeing is pure private sector, and particularly if they’re not a registered endocrinologist, then think twice. Think three times.

Given testosterone’s key role in men’s health, why are there still so many cultural misconceptions, such as testosterone’s links to aggression?

People talk about environments as being “infused with testosterone”. One example is like a Futures Exchange, with the guys in blazers shouting, “Buy, buy, buy!” But a fantastic study was done 5-6 years ago, which brought in people from all sorts of different fields, from endocrinology to trading to game theory to psychology and statistics. They simulated this trading behaviour. And they found that if you started off with a high level of testosterone, or it rose a lot during trading, or you received some testosterone treatment before trading, you made what superficially seemed to be some rash calls on the market.

But drilling this down, it was not that testosterone that was making you rash or irresponsible. It simply altered how you perceive the future. So testosterone, in this context, made you perceive the future as more benign or more favourable. You were seeing the world through rose-tinted spectacles. So these decisions were made from a circuit of optimism, rather than through gung-ho risk. The idea that testosterone is linked to aggression, we have no idea where this has come from. And it is not just out there in the lay field, but also in the medical field. And if you actually look at the evidence, there is nothing.